Jay-
With an LCD, there is a layer of liquid crystals sandwiched between two layers of transistors. A protective glass or polycarbonate plate covers the whole thing. Behind all of this is a reflective layer.
When an electric current is applied to the liquid crystal, the liquid crystal in that pixel uncoils, allowing light to reflect off of the reflective backing. In low-light situations, that light must be provided by backlights, which are thin cathode tubes (not unlike a fluorescent light) mounted, typically, on the sides and the top of the screen, out of view. Their light reflects off the back of the screen and out of any pixel in which the liquid crystal is uncoiled.
It used to be (as in my PowerBook 520) that if you sat with the sun at your back, the sunlight would work as effectively as the backlighting. It entered the screen and reflected off the reflective layer where crystals were uncoiled. Nowdays, however, that cannot take place. When you sit outside, the pupils of your eyes "stop down", so to speak. Since the backlights in the LCD are much dimmer than the ambient light from the sun, it cannot possibly compete in terms of brightness with the ambient light and so it is difficult to see.
In earlier LCDs, the sun itself could provide the light to reflect and so the brightness <i>could</i> keep up with ambient light--they came from the same source-the sun!
My guess is that somehow ambient light can no longer enter the LCD from the front. I have no idea why.
